Curiosity result could confirm Mars life, says Levin

As space fans anticipate news of organic molecules from the Mars Curiosity rover – cryptically teased by the mission's chief scientist, John Grotzinger, in a US radio interview – there's one man who is even more excited than most.

Former NASA researcher Gilbert Levin says that a positive sign of organics by Curiosity would confirm his claim that NASA has already seen evidence for life on Mars – from an experiment called Labeled Release that went to the Red Planet aboard the Viking mission.

If Curiosity has found evidence for organics, as many are hoping, "that removes the last barrier to my interpretation of the Labeled Release results, and leaves us free and clear", Levin told New Scientist.

Though the prospect of new Curiosity findings have set the internet abuzz, nobody from NASA has yet said publicly what they are: Grotzinger has refused to elaborate, pointing New Scientist, and other journalists, to a presentation scheduled for the American Geophysical Union annual meeting in San Francisco, which begins on 3 December.

'History books'

Grotzinger's key comment to US National Public Radio – "this data is going to be one for the history books. It's looking really good" – concerned an instrument called SAM, for sample analysis at Mars, which, among other things, is tasked with finding organic molecules in the Martian soil.

That's because the failure to detect any organics at all by an instrument aboard the Viking lander was the counter-evidence that cancelled out an apparent detection of active biology by Levin's Labeled Release experiment. That experiment showed that radioactively labelled carbon from a nutrient solution added to the soil was released into the air in the test chamber – an apparent sign of metabolism.

Though Levin has long argued otherwise, the consensus has been that Viking did not find evidence of life on Mars.

Caution urged

Levin acknowledges that, after more than three decades of argument over what the Viking results really mean, opinions are not likely to change overnight, no matter what the new Curiosity results may show. Although proving the presence of organics in the soil will "remove all rationale against" his interpretation, he says, "it's hard to change a paradigm". Most scientists are convinced that Viking's results were inconclusive. "I doubt this will change the consensus" he adds.

Chris McKay of the NASA Ames Research Center in Moffett Field, California, is a leading researcher on the possibility of life on Mars, and he, too, urges caution. "This is probably not as exciting as the internet rumors suggest," he says – as someone who is privy to what Curiosity has found.

Then again, McKay was never convinced that Viking failed to find organics. He has argued, in a peer-reviewed paper, that the Viking non-detection of organics was invalid, by demonstrating that soils from the Atacama desert in Chile, known to contain organics, showed no signs of them in a test that replicated the one on Viking.

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